Acrylic pressure-sensitive adhesives are excellent in properties such as weather resistance and are widely utilized as pressure-sensitive adhesives forming pressure-sensitive adhesive layers in various pressure-sensitive adhesive sheets. Among the acrylic pressure-sensitive adhesives, since a water-dispersion type acrylic pressure-sensitive adhesive using a water-dispersion type acrylic polymer does not use any organic solvent as a solvent unlike a solvent-type acrylic pressure-sensitive adhesive, the water-dispersion type acrylic pressure-sensitive adhesive has advantages that it is desirable in view of environmental health and also is excellent in view of solvent resistance. In general, in the case that the acrylic pressure-sensitive adhesive is constituted by an acrylic polymer alone, it is difficult to obtain sufficient pressure-sensitive adhesive properties such as a high adhesiveness and hence a tackifying resin is added thereto in order to impart such properties. However, when the pressure-sensitive adhesive tape manufactured with adding a tackifying resin is used at fixing automobile parts such as interior materials for automobiles for a long period of time, there arises a problem that there is observed a so-called “fogging phenomenon” wherein volatile components in the pressure-sensitive adhesive tape attach to windshield and the like to cause fogging.
On the other hand, though it is a case different from the cases of pressure-sensitive adhesives or pressure-sensitive adhesive tapes, a method for reducing the occurrence of the fogging phenomenon has been proposed in “adhesives” used for adhesion of interior materials for automobiles [cf. JP-A-2003-327938 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)]. Specifically, in an adhesive comprising a styrene-based block copolymer as a main agent, there has been proposed a method for reducing the occurrence of the fogging phenomenon by regulating a ratio of components having a molecular weight of 400 or less in the total composition constituting the adhesive to less than 7% by weight.
However, such a method for reducing the occurrence of the fogging phenomenon is relevant to a hot-melt adhesive. Therefore, it is necessary to melt the adhesive by heating or the like at adhesion operation and thus a step for melting the adhesive, such as heating, is required. Recently, in the assembly line of automobiles, it is increasingly required to shorten operating time and hence pressure-sensitive adhesive tapes with which the adhesion operation can be performed without requiring a means of heating or the like have been increasing employed. However, as mentioned above, in the case that conventional pressure-sensitive adhesive tapes are used for adhesion of interior materials for automobiles, the generation of the fogging phenomenon is regarded to be problematic. In particular, as the amount of the pressure-sensitive adhesive tapes used per one automobile increases, a pressure-sensitive adhesive tape exhibiting a reduced occurrence of the fogging phenomenon has been desired.